Conformational flexibility of chitosan: a molecular modeling study.

Chitin and chitosan are naturally occurring polysaccharides composed of β-(1,4) linked N-acetylglucosamine units (GlcNAc) and, for chitosan, also glucosamine units (GlcN). In recent years, chitosan has attracted much interest because of its special physical and chemical properties related to drug delivery, wound healing, and tissue engineering. However, limited structural knowledge is available for chitosan because of its composition of the randomly mixed building blocks, GlcNAc and GlcN. In this study, we present exhaustive combined molecular dynamics and Monte Carlo simulations that unravel the conformational flexibility of the β-(1,4)-linkage in di-, tri-, and tetrasaccharide models of chitin and chitosan. The most flexible disaccharide unit was found to be GlcN-GlcNAc, populating four conformations. Furthermore, it is found that the conformational freedom of a glycosidic bond is independent of the flexibility of the neighboring linkages along the oligomer. The results are interpreted with respect to hydrogen bond formation and implications for polymer properties.